Field of the Invention
Embodiments of the inventions relate to user input buttons and keyboards comprised thereof. More particularly, embodiments of the invention relate to magnetically biased keys, including those with a high degree of parallel motion.
Background
Keyboards of various types are ubiquitous in today's technological arena. Important factors in a keyboard's usability are its size and feel to a user. High end computer keyboards employ a vertical bearing shaft to ensure parallelism as the key is depressed. However, such structures are impractical for low profile keyboards common on laptop computers or for use with other mobile devices. The current commercial state of the art in low profile keyboards uses a plastic scissor mechanism to control the motion of a key during actuation, and a rubber dome to provide a spring force. For small keys, the scissor mechanism generally provides sufficient parallelism, so that there is relatively little tilt from side to side as the key is actuated, which does not significantly impact usability. However, with larger keys such as the shift, return, and space bar keys, the plastic scissor mechanisms tend to flex, resulting in uneven actuation or jamming. To combat this, contemporary designs add metal support bars which improve the parallelism. These bars transfer actuation force from where the key is pressed to the remote end of the key. This acts to pull down the remote end and limit the tilt of the key during actuation, thereby improving parallelism. Unfortunately, these metal bars, (which generally run along two sides of the key), also increase part count, mechanical slop, weight, and noise, all of which reduce the precision of motion and the quality of feel for the user. Depending upon the size, stiffness, and precision of these bars, a key may still exhibit residual tilt when actuated off-center. Moreover, the loss of parallelism is exacerbated as the key increases in size.
Even for the smaller keys, the “fingertip feel” or tactile sensation of actuating the keys deteriorates as the finger senses the imperfections in the mechanism. Further, the current practice of scissor plus rubber dome architectures produces a mushy feel at the end of their travel. This is due to a small cylindrical rubber nib at the center. of the rubber dome. The nib is designed to apply pressure to a membrane switch below the dome. As the nib compresses, it creates a spongy, less crisp feel. Development of a key which eliminates these deficits and provides an improved feel for low profile keyboards is desirable.